Photographic process and composition



Patented Dec. 7, 1943 UNITED rno'rocnarmo rnocass AND Y comosrrron Virgil B. Sease, New Brunswick, and George A. Dawson, Stelton, N. 1., assignors, by mesne assignments, to E. I. du Pont de Nemours &-Company, Wilmington, Del., a corporation of Delawere No Drawing. Application August 2, 1940,

Serial No. 350,092

llclaims. (Cl. 95 -2) This invention relates to photography. More particularly it relates to novel toning baths for photography. The invention further relates to processes for producing colored images in photographic "elements. In one of its important aspects it pertains to the processing of multilayer photographic elements especially photographic films to multi-color pictures.

This invention has for an object the production of a novel yellow toning bath. A- further object is the production of a stable toning bath which can be used over a long period of time, A still further object is to produce a. toning bath which can bequickly and. economically produced. A still further object is to produce a toning bath from readily available starting materials.

treating baths may vary considerably.

Another'object of the invention is to provide I novel processes for producing colored images in multilayer film. A further object is to provide I an improved and simplified process for toning the yellow color. component image-for multicolor photography. A still further object is to provide a process for rendering one image'component of a photographic element inactive to color-forming development while another component is being color-developed.

The above objects are accomplished in accordance-with the hereinafter described invention by the preparation and use of an aqueous solution of a water soluble cyanide and a water soluble salt of a heavy metal which forms a yellow sulfide and/or telluride. By water soluble cyanide is meant the salts of hydrocyanic acid which are soluble to an extent of at least 1.0% in water. Suitable-compounds falling within this category are the amine, ammonium, substituted ammonium and alkali metal salts of hydrocyanic acids. The alkali metal salts constitute the preferred embodiment of the invention.

The expression "water soluble salt of a heavy metal which forms a yellow sulfide" is meant the salts which are soluble to an extent of at least 1.0% in water. Suitable metals falling within of organic or inorganic type. Thust'he above water-soluble heavy metal salts of sulfuric, phosphoric, nitric, boric, hydrochloric,-hydrobromic,

hydroiodic, acetic, propionic, etc., acids may be used. Among the compounds falling within the class specified are cadmium sulfate, cadmium nitrate, cadmium fluoride, cadmium chloride,

cadmium bromide, cadmium iodide, cadmium 55 borotungstate, cadmium selenate, cadmium acetate, and cadmium lactate.

The amount of the salt' present inthe aqueous From 5 to 20 parts of thehydrocyanic salts per parts of water represents apractical range and 7 to 10 parts, a preferred range; From2 to 12 parts of the heavy metal salts per 100 parts of water represents a practical range and 3 to 8 parts, a preferred range. 7.

When baths of a the above type aie used for toning photographic elements containing metallo-sulfur or metallo tellu'rium complex images, yellow images of good strength and color are obtained. A photographic element containing a verted to a silver sulfide image. This may then be treated in an'aqueous bath of the abovedescribed type containing a water soluble salt oi hydrocyanic acid: and awater soluble salt of a heavy metal capable of forming a-yellow sulfide to form a yellowtoned image.

The bleaching {of silver images is well known and itself formsno part of the present invention. They may be bleached to a reducible form by the use 01' a bleach bath containing copper chloride or bromide and an oxidizing agent such as chromic acid, potassium ferricyanide, potassium ferricyanide in the presence of alkali carbonate, etc. The bleached image is then converted into a silver sulfide or telluride or complex image by treatment with a water soluble sulfide or telluride. or water-soluble reducing-sulfur or tellurium compound capable of forming a silver sulfide or telluride. Suitable compounds are hydrogen sulfide, the alkali metal sulfides, e. g. sodium sulfide, potassium sulfide, barium sulfide, ammonium sulfide, etc., sodium thiomolybdates, thiotungstates and thiostannate's, sodium selenide, and similar'compounds of which the alkali metal sulfides and hydrogen sulfide are preferred.

The; silver images which are bleached may be positive or negative images or may be reverse images. These images may bequite complex in their chemical constitution and consequently the subsequent sulfide or selenide images maylike- 'wise be complex. This may be due to the fact that a bleached image is formed from a developed silver image in a fixed emulsion layer. In the developing step, two images are always formed, viz., .one of metallic silver and the othera residual stain image, sometimes called a secondary image, or -restbild, representing the organic oxidation products of the developing agent or agents, possibly admixed with some colloidal sium ferricyanide, the bleached image, in toto,.

is not entirely silver ferrocyanide but a complex image containing probably some organic complexes. Thus, sulfiding such a bleached image will result in a silver-sulfur complex image rather than in plain silver sulfide. Hence, the expressions "silver sulfide and silver selenides images are meant to cover the complex images as well as the substantially pure images,

The novel coloring or toning baths hereof may be used in various manners with diverse types of photographic elements in the manners hereinafter set forth. Photographic silver pictures. for example, may be colored or toned and intensified by converting the silver in said pictures into reducible silver compounds which are transformed into silver sulfide or telluride images and the latter treated in the above-described baths to form yellow images. The water soluble products are washed out at each stage of the process.

An important use for the baths is in reversal image colored or toned yellow. A latent image which may be the negative image from an orig-' inal scene' or a positive image printed from such processes where it is desirable to have the reverse photography thus may be successfully processed in accordance with this invention. In such processes of producin colored images. one of the ima e records is bleached. converted to a silver sulfide or selenide image. and thus made inactive to later process ng of other images or color records. The inactive layer is then toned in the above-descr bed toning baths to form a yellow image record.

In producing col red ima es in a binack or monopack the yellow ima e record preferably is formed in the outer layer of the multi a er element and this layer is rendered inactive by conversion to sulfide or the like ima es. After exposure of the 'bipack or monopack in a camera to light controlled by an object to be reproduced which may be an original scene or a color transparency the blue, green and red records which are formed in the respective emulsion layers are then developed in a nonhardening, non-colorforming developing bath, fixed and washed, which results in color records in terms of metallic silver in the'difierent layers. The outer color component ima e layer of the multilayer photographic element is then bleached by a controlled bleaching process and the bleached silver image converted to a silver sulfide. or selenide image. This image layer is rendered inactive, which enables the remaining layers or color component records to be transformed into colored images,

conversion of the layer to the inactive form may take place prior to a color-development step or subsequent to a color developmentv step.

The invention as previously indicated is not limited to the treatment of any-particular type of multilayer photographic elements. Two or more layers differentially sensitized may be placed upon the same side of a transparent support. For in the case of a monopack two layers may be on one side and one on the other, or three layers may be superimposed on one side. In the case of a bipack, two layers may be placed on one side of a transparent support, or one layer may be placed on each side thereof.

The layers are arranged and sensitized so that their utilizable sensitivity for color recording is about one third of the visible portion of the spectrum. Various cyanine,- carbocyanine, pseudocyanine, neocyanine, cyazine, earbocyazine, etc., rhodanine sensitizers in the form of their bases or salts may be resorted to.

Another important aspect of the invention is concerned with the color-processing of films which contain prefogged layers between differentially sensitized layers, which form black barrier layers upon the first development thereof. These novel elements are described in U. S. Patent 2,191,502, and comprise a transparent base having at least two difierentially sensitized emulsion layers superimposed thereon, one of the layers being imposed directly on the base and a layer of prefogged silver salts interposed between said emulsion layers. More particularly, they comprise a transparent base having three differentially sensitized emulsion layers superimposed thereon, one of the layers being imposed directly on the base and a prefogged layer between each of the said emulsion layers. The outer layer, that is, the one which faces the object to be reproduced is blue sensitized and preferably contains a yellow filter dye, a green sensitive layer forms an intermediate layer and a red sensitized emulsion layer is imposed directly on the base.

A modified construction utilizing a green blind These elements are color processed similar to elements which form no barrier layers, but their processing is much simpler because no re-exposing light can pass between layers. The films are developed in an ordinary developer such as Metol hydroquinone. The innermost layer is color-developed the proper color which with certain constructions may be blue-green, the outer layer is rendered inactive. e. g. with sodium sulfide and the middle layer is exposed. It is preferably chemically exposed by bathing the film ina solution of a mild inorganic reducing agent, e. g. 0.5% aqueous solution of alkaline sodium arsenite or a 5% aqueous solution of hydrogen peroxide. This chemical exposure will make sensitive the silver salts remaining in the middle layer.

As another means of chemical exposure the film may be treated with an aqueous solution of an organic sulfur-bearing compound such as a 5% aqueous solution of guanidine thiocyanate or guanyl thiourea, thiourea, allyl thiourea, imino imino sulfinic acid of a pH of at least about 7.1.

It is not necessary, however, to resort to chemical exposure of the middle layer to render it exposed or so that the silver salts are sensitized.

Thus, the middle layer may be exposed by means of X-ray exposure of the entire film, or by means of mechanical vibrations of a class known as ultra-sonic vibrations. In the latter case the entire film, during the latter part of the washing operation following the yellow development, may be subjected to ultrasonic vibrations, or the film, after washing may be immersed in water or some non-film solvent and then subjected to ultra-sonic vibrations. The central layer can also be exposed by means of heat rays, in which case the entire film should be immersed in formaldehyde solution before exposing to the heat rays.

The silver images produced by the just-described procedures may be then removed with an alkaline ferrlcyanide solution followed by fixing in a hpyo solution containing sodium thiosulfate solution.

The novel coloring or toning baths. may be prepared in variousways by admixing the components, water, the water-soluble salt of the hydrocyanic acid and the water-soluble salt of cadmium, arsenic, antimony. The two salts may be mixed and admixed with the water or admixed separately with the water. Various loading agents which are neutral in their reaction may be incorporated in the bath to control the penetration thereof. Suitable substances include mono and polyhydric alcohols, e. g. methyl, ethyl, n-propyl, isopropyl, butyl, amyl, glycerol, ethylene and propylene, glycol, etc.; acetone and its homologues, gelatine, gum arabic, etc. in water,

This was prepared in the same manner as in Example I. A similar bath was prepared by using the nitrate in place of the chloride.

Eeample V Antimony nitrate -grams- 40 Potassium cyanide do 80 Water to er" 1 This was prepared after the manner of Example I.

Example VI Cadmium acetate grams .70 Potassium cyanide ..do 120 Water tn a liter 1 ilycerine cs 180 various solids such as sugar, sodium sulfate and I sodium ,chloride. retardants may vary widely from 2 to 500 parts, for-instance, of the aqueous solution representing a practical range. Y

The invention will be further illustrated, but

The amounts of these inert The above bath was prepared by adding the salts to 500 ccs. of water, then adding the glycerine with agitation and finally bringing the total volume up to 1 liter. a

In place of the specific, retardants of Example VI, may be substituted others including those specified above.

The coloring and toning baths'hereof especial- -ly those containing cadmium salts are remarkably stable and may be used for relatively long periods of time. Thus, the invention constitutes a distinct contribution to the art because prior toning baths are quite unstable. .The known cadmium salt toning baths are notoriously unstable.

The following examples relate to "Iocesses of colorphotography wherein the above baths are utilized.

Example VII A low opacity silver image is bleached to a reducible silversalt form by a chromic acid and sodium chloride or an alkaline-ferrocyanide is not intended to be limited bythe following examples wherein the parts stated are parts by weight.

The first six examples are directed to the novel toning baths hereof.

Example! A coloring and toning bath of the following composition was prepared by adding the ingredients to water with slight agitation:

Cadmium sulfate grams 30 Potassium cyanideur. do 80 Water to (H liter 1' "Example II A. coloring and toning bath of the following composition was prepared by adding the ingredients to water with slight agitation:

, Cadmium nitrate grams 40 Potassium cyanide do 100 I Water er" 1 Example II? Cadmium aoetate. grams 35' Sodium cyanide do 120 Water to i er-' 1.

A bath of the above constitution was prepared after the manner'of Example I.

Example IV Arsenious chloride grams Ammonium cyanide do 80 Water to liter Sodium sulfide grams 20 Ethyl alcohol ccs 400 Glycerine ccs 400 Water to liter. 1

plain gelatine as an anti-abrasion layer.

bleach bath. The film is washed thoroughly to remove all water soluble compounds. The film is then treated in a bath of the following composition for about 1 minute: v

The silver images are removed with Farmer's reducer and the resulting film is treated in the bath of Example I, and washed. A yellow colored image which is an excellent minus-blue results.

Emample VIII r A transparent gelatine subbed cellulose nitrate film support is coated on one side with a 50 mg. coating of positive type 'gelatino silver bromide emulsion containing tartrazine as the yellow screening dye. Over this is coated a thin layer of The other side of the fllm' base is coated with a 50 mg. layer of panchromatized gelatino silver chloro-bromide emulsion. Over this is coated a thin layer of plain gelatineand over this is ap of a filtered exposing light transmitting no bluegreen rays.

Copper sulfate grams 100 Sodium chloride do 100 Sulfuric acid conc h cc 25 Water to liter 1 4. Washed and dried. 5. Float multicoated side for 45 seconds on:

Sodium sulfide grams 20 Ethyl alcohol cc 400 Glycerine cc 400 Water to liter 1 and. wash.

6. Float'multicoated side 10 minutes on magenta color-forming developer:

P-aniiniodiethylaniline hydrochloride grams 4 Sodium sulfite anhy do 3 Sodium carbonate, anhy do 25 4% alcoholic sol of phenyl-methyl-Pyrazolone s.. 5 Water to liter 1 7. Wash and then float the single emulsion layer side minutes on a blue-green color-forming developer:

p-Aminodiethylanilinehydrochloride grams 4 Sodium sulfite, anhy do 3 Sodium carbonate, anhy do 25 4% Alcoholic soln. of 4-chlor-O-phenyl phenol cc 5 Water to lifer 1 The silver images developed by the color developers are then removed by treatment with alkaline ferricyanide solution followed by fixing in plain 25% aqueous hypo, sodium thiosulfate solution.

The film now contains magenta and blue-green dye image records and a yellow image record comprising a silver-copper sulfide complex salt. The exact nature of the silver-copper-sulfide compounds produced by treating silver images with a copper salt in the presence of a halogen ion is not definitely known and the color of this image varies from yellow to brown depending to some extent, on the relative amounts of copper-to-silver in the bleached image.

Usually the greens and reds produced by the above outlined process are not of suflicient brilliancy or saturation. In such cases, the silver-.

Cadmium sulfate grams 30 Potassium cyanide do 80 Water to liter 1 in which the film is treated for 3-4 minutes, then simply washed and dried.

The step of-converting one of a numberof mutually-supported, non-interpenetrating, silver images into a form wherein it is not affected by subsequent processing steps, or rendering it inactive to such steps, yet remaining in such a form wherein it can be converted into a color image representing one of the 3-color subtractive process colors, makes possible a simplified and convenient method for the reversal processing of multilayered films to positive color pic tures.

Example-IX A transparent film base, suitably subbed, is provided with a 90 mg. coating of gelatino-silver bromide emulsion sensitized predominately in the orange-red region, but not the green region, by means of naphthiocarbocyanine in the presence of soluble bromide. Over this is coated a 50 mg. layer of ordinary positive emulsion mixed under ordinary room illumination and thus is highly fogged. Over the fogged barrier layer is coated a layer of gelatino silver chloro-bromide emulsion sensitized into the green region with erythrosine or pinaflavol. A 60 mg. coating of plain gelatine containing Tartrazine O, C. I. #640, as the yellow screening dye is applied to form a filter layer. Over the filter layer is applied a 50 mg. coating of ordinary positive type; gelatino silver bromide emulsion. The film is exposed in a camera to a natural colorscene, either an original or a natural color transparency. The steps of processing such a film are as follows:

1. Develop 10 minutes in a positive type Me'tolhydroquinone developer, 8. suitable formula be- 'ing:

Metol ramsfi 1.5 Sodium sulfite, anhy do 60.0 Hydroquinone do 5.0 Sodium carbonate, anhy .410... 48.0 Potassium bromide do 1.6 Water toliter 1 '2. Wash 3. Flash through the base with red or white light to re-expose the innermost layer.

4. Develop in blue-green color-forming developer.

t 5. Wash and dry in ordinary room illuminaion 6. Treat 3 /2 min. in 90% aqueous ethyl a1- cohol saturated with sodium sulfide.

'7. Wash 8. Develop in magenta color-forming developer 9, Wash 10. Bleach in alkaline potassium ferricyanide, wash and fix in 25% plain hypo solution 11. Wash silver halides remaining in the outermost layer after the blue-green color-development of the innermost layer, were converted to silver sulfide and/or silver-sulfur complex salts. These salts were not redevelopable and were not influenced by the subsequent photographic processing of the other layers to color-images. After the magenta images had been formed, the metallic silver images can be removed and the film fixed, all without disturbing the undevelopable silver-sulfur complex'images. At the appropriate stage in the processing, however, these images can be converted to color-images by processing baths which have no adverse eflfects on the dye images already formed. In fact, after the cadmiumcyanide bath treatment of the entire film, the dye images appear to have greater brilliancy.

The film resulting from the above processing can'ies differently colored dye images in the two inner layers and inorganic pigment color image, represented by the silver-cadmium-sulfur complex, in the outer layer. The colors of the original scene are exceptionally well reproduced by this process inasmuch as the yellow images are truer lemon-yellow (minus-blue) than those pro-I duced by color-forming development. Inasmuch as the yellow images bear much of the color- ,responsibility for producing good greens from Example X A film such as described under Example VIII is processed as indicated therein except that ammonium sulfide is used in step 5 in similar amount to convert the outer image into the inactive state. The ammonium sulfide solution is prepared by. passing hydrogen sulfide into 750 cc. of concentrated ammonium hydroxide until saturated, then add 1200 cc. of ethyl alcohol.

Example XI A film such as dmcribed under Example IX is processed'in a similar manner except that in step'fi a solution of barium sulfide to which has been added an equal volume of methyl alcohol is substituted for the sodium sulfide and ethyl alcohol.

' In the foregoing examples, the inactivity of silver sulfur-complex images in emulsion layers which have been fixed has been utilized in processes where the emulsion layer is subjected to developing operations after the formation of the silver-sulfur complex. The additional inactivity of silver-sulfur complex images in the presence of ordinary photographic fixing baths can likewise be utilized in the processing of multilayer films to color-component records as will be hereinafter described, in the following examples.

In co-pendlng application Serial No. 132,144, of Sease and White, filed March 20, 1937, there are described methods of developing and printing multilayer film elements. More particularly a bipack film combination; wherein one element carries at least two differently color-sensitized silver halide layers, is processed to produce 3 separate, individual color-component records. Such processes represent an extension of .a bipack into three color component records. In aforesaid copending application, in one modification, only the outer image of the multilayered element of the bipack is reformed after bleaching both developed silver image records. In another modification thereof, only the inner is reformed by,

development. By utilization, however, of the principles of the present invention wherein a layer preferably the yellow aspects of the scene is assao'm 5 of extending the color component records of a bipack to 3 individual colorrecords is greatly simplified. This isillustrated in the following examples.

Example XII Carmosin M and on this is coated a green sensitlve photographic layer. The latter emulsion is in contact with the emulsion surface of the front film and all sensitive layers "are of the wellknown silver halide gelatine emulsion type. Upon exposure to a natural or colored scene all color records are formed simultaneously; the blue record is formed in the emulsion layer of the rear film, the green record is formed in the top layer of the front filmand the red record is formed 'ish silver-sulfur complex image in the outer layer. This image, although of low visual opacity, has

alkaline potassium ferricyanide solution.

6. Wash and dry.

7. Treat film one minute with all/1100130110 sodium sulfide solution:

Sodium sulfide. grams-.. 2 Water M 150 Ethyl alnnhnl or 850 The time of this treatment varies depending on the coating thickness and hardness of the emulsion layer and the relative density of the original silver record formed therein. In some cases, 30 seconds is sufiicient while thicker emulsion layers may requireas long as 1% minutes for the sulfide solution to penetrate to the depths of the layer. p

8. Wash.

9. Fix, wash and dry.

The multilayer film now carries only a yellowa high printing opacity to blue-sensitive positive emulsions. It is now printed in register with the positive print made in step No. 4. The resuiting developed print represents a negative image representing the color-component record originally established in the inner emulsion layer of the front film of the bipack combination. The second color-component record is represented by the yellow complex image and the third color record is on the rear film of the bipack.

Example XIH ample XII the color-component record of the inner emulsion layer of the front film is reformed.

- The processing steps of the exposed bipack films are as follows:

rendered inactive and consequently the processes 15 Steps 1 to 6 same as in Example Kg.

'5. Bleach the silver images of the rear film in 7. Remove outer image of rear film by treatment with concentrated sodium thiosulfate solution whereby a control of penetration as described in U. S. Patent 2,166,617 is obtained.

8. Treat remaining bleached silver images 3 minutes with a saturated aqueous solution of barium sulfide.

9. Wash and dry.

The individual color component records can then be prepared by combination printing as described in Example XII.

In place of'the specific aromatic amino developing agents described in the preceding examples may be substituted various other specific agents of this type. These agents have an unsubstituted amino group which apparently enables the oxidation product to couple with the color-forming compoundu Such agents include the diand triamino aryl compounds in which one amino group is in the ortho or para position to another amino group, and the compounds formed therefrom by substitution in the amino group as well as in the ring. Thus, halogen, alkyl, alkoxy and aryl groups may be present.

The preferred developing agents in the'process of dye coupling development are derivatives of p-phenylenediamine and particularly the asymmetric dialkyl p-phenylenediamines of 1 to 4 carbon atoms, e. g. p-aminodimethylaniline, p aminodiethylaniline, p aminodibutylaniline, etc. Other developing agents which may be used include p-phenylenediamine itself, p-methylaminoaniline, p-ethylaminoaniline and p-aminophenol, N,N-di-ethyl-o-phenylenediamine, chloro-p-phenylenediamine, 1,2,5-toluylenediamine, 2 amino 5 5 diethylaminotoluene, N-p-aminophenylpiperidine, N-methyl-N-hydroxyethyl-pphenylenediamine, N-butyl-N-hydroxyethyl-pphenylenediamine, 2-amino-5-(N-butyl-N-hydroxyethyl) aminotoluene and its dihydrochloride, B-q-dihydroxypropyl-pephenylenediamine, 4 :4 -diamino-di-phenylamine, 4 4' -diamino-2' hydroxy-diphenylamine, etc. These aromatic amino-developing agents are in the form of their organic or inorganic acid salts and may be used in the preparation of the developing solutions. The salts are in general more stable than the free bases. As examples of suitable salts mention is made of the hydrochloride, sulfates, acetates, etc.

Likewise, other color forming compounds or mixtures may be substituted for the specific ones set forth in the above procedures and color developer baths.

Suitable magenta color-formers include nitriles, e. g. p-nitrobenzyl cyanide, o-nitro-benzylcyanide, p toluyl acetonitrile, w-cyanoacetyldibenzfuran, w-cyano-acetylacenaphthene, 1-wcyano-acetylcoumarone, 1:3-di- (w-cyanoacetyl) benzene, acyl nitriles, e. g. cyanac'etophenone, methoxy-a-naphthoyl-acetonitrile, cyanacetanilides, e. g. 1-cyanacetaminobenzthiazole, etc., phenyland naphthyl-methyl-pyrazolones, e. g.

l-phenyland 1-naphthyl-3-methyl-4-pyrazo-' lone.

Suitable blue-green color formers include phenols, e. g. ortho and meta-chlorophenol, o-bromophenol, o-iodophenol; naphthols, e. g. 2,3,4-trichlornaphthols, 2,6 dibromo 1,5 dihydroxy naphthalene, etc. Other color-formers will be apparent to those skilled in the art.

- This invention has a, number of distinct advantages which are self-evident. An important advantage resides in the fact that it enables one to effectively inactivate a layer of a multilayer film to ordinary processing baths so that the remaining layers may be processed to color images.

A further advantage resides in the fact that it enables one to combine color developing and toning processes.

Another advantage resides in the fact that the invention enables one to produce colored images which involve only one step of controlled penetration.

A still further advantage resides in the fact that a stable, easily prepared, yellow toning bath may be economically prepared.

Another advantage resides in the fact that it enables one to provide a true minus blue or lemon-yellow color record in a multilayer film containing color developed images.

As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that we do not limit ourselves to the specific embodiments herein except as defined by the appended claims.

We claim:

1. A photographic coloring and. toning, bath comprising an aqueous solution containing a water-soluble salt of hydrocyanic acid and a water-soluble salt of cadmium.

2. A photographic coloring and toning bath comprising an aqueous solution containing from 5 to 20 parts of a water-soluble salt of hydrocyanic acid and from 2 to 12 parts of a watersoluble salt of cadmium.

3. A composition as set forth in claim 1 containing an inert diffusion retarding agent for controlling the penetration of the bath.

4. A composition as set forth in claim 2 containing an inert difiusion retarding agent for controlling the penetration of the bath.

5. y The process which comprises treating a photographic element containing bleached silver images in a. bath containing a water-soluble reducing compound selected from the group consisting of sulfur and selenium reducing compounds capable of forming an insoluble silver compound image taken from the class consisting of silver sulfide and silver selenide images and treating the resulting element in a coloring and toning bath comprising an aqueous solution containing a. water-soluble salt of hydrocyanic acid and a water-soluble salt of cadmium.

6. The process which comprises treating a photographic element containing bleached silver images in a. bath containing a water-soluble reducing compound selected from the group consisting of sulfur and selenium compounds capable of forming an insoluble silver compound image taken from the class consisting of silver sulfide and silver selenide images and treating the resulting element in a coloring and toning bath comprising an aqueous solution containing an alkali metal cyanide, and a water-soluble salt of cadmium.

'7. The process which comprises treating a photographic element containing bleached silver images in an aqueous bath containing an alkali metal sulfide, and then reacting the resulting silver sulfide images in an aqueous bath containing an alkali metal cyanide and a water-soluble salt of cadmium.

8. The process which comprises treating a pho"- tographic element containing at least two superimposed layers containing different color component records as metallic silver images with a.

bleaching agent, converting the bleached silver salt. images in the outer layer thereof to silver 9. The process which comprises treating a photographic film element comprising a transparent base having superposed on one side a green color separation record and ablue color separation record and on the reverse side thereof a red color separation layer, said records being in the form of exposed silver salts, developing exposed silver salts of such records in an ordinary photographic developing solution, fixing out the undeveloped salts, bleaching each silver image record to a silver ,salt image, converting the silver salt of the blue layer to a silver sulfide image, color developing the silver salts of the green layer to a magenta color, color developing the silver salts of the red layer to a blue-green color, removing the silver images and converting the silver sulfide image layer into a cadmium sulfide image by, treatment with an aqueous solution containing a water-soluble cadmium salt.

. 10. A method of color photography which comprises exposing a photographic element comprising a transparent base having three silver halide emulsion layers sensitized red, green and blue respectively, superposed thereon, the red layer being imposed directly on the base, a prefogged silver salt layer interposed between each of the emulsion layers and a yellow filtering layer positioned in front of said red sensitized layer, developing said element with a non-color formingdeveloper, whereby silver images are formed in said emulsion layers andopaque barrier layers are formed, exposing the red layer to light and color developing the silver salts in the red layer,

converting the silver salts in the blue layer to an insoluble silver compound image taken from the class consisting of silver sulfide and silver telluride images, color developing the green layer and treating the'insoluble silver compound image layer in an aqueous solution containing a watersoluble salt of a hydrocyanic acidand a watersoluble salt of a heavy metal taken from the group consisting of arsenic, antimony and cadmium which is capable of forming", a yellow compound taken from the class consisting of sulfides and selenides.

11, A method of color photography which comprises developing a monopack comprising a transparent base, a green sensitized silver halide emulsion layer imposed directly on saidbase, a prefogged silver salt layer imposed on said green layer, a green blind panchromatic emulsion layer imposed on said prefogged layer and a blue sensitiz'ed emulsion layer imposed on said panchromatic layer which has been exposed to a color scene, with a non-color forming developing agent, exposing and color developing said green sensitive layer, converting said blue layer to an insoluble silver compound image taken from the class consisting of silver sulfide and silver selenide images, treating the insoluble silver compound image layer in an aqueous solution containing a Water-soluble salt of hydrocyanic acid and a water-soluble salt of a heavy metal'taken from the group consisting of arsenic, antimony and cadmium which is capable of forming a yellow compound taken from the class consisting of sulfides and selenides, exposing and color developing the green-blind layer and removing the silver deposits from all layers.

' VIRGI B. SEASE.

GEORGE A. DAWSON. 

